Apparatus and method for determining a state parameter of an object to be monitored

ABSTRACT

An apparatus for determining a state parameter of an object to be monitored includes a means for providing a plurality of measurement values, wherein the measurement values include information relating to the state parameter of the object to be monitored, a comparison means for comparing the measurement value to a predeterminable comparison parameter, wherein the comparison means is formed to output a first comparison signal when a predeterminable number of measurement values falls below the comparison parameter within a measurement interval, or to output a second comparison signal when the predeterminable number of measurement values exceeds or reaches the comparison parameter, wherein the first comparison signal or the second comparison signal indicate the state parameter.

REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/072,099, filed on Mar. 4, 2005, entitled, “Sampling Apparatus andMethod for Determining the Driving State of a Vehicle,” that claimspriority to German Patent Application No. 102004010665.7, that was filedon Mar. 4, 2004 and is incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to a system for determining a stateparameter of an object to be monitored, wherein the state parameterindicates a physical state of the object.

BACKGROUND OF THE INVENTION

In a determination of a state parameter of an object to be monitored,there is often the question of the reliability with which the stateparameter has been determined. The state parameter indicating a physicalstate of the object to be monitored is often determined based on acomparison of measurement data with a threshold. If, for example, themeasurement data are noisy, there can be wrong decisions in thedetermination of the state parameter, so that a possible subsequentdecision chain based on an erroneously determined state parameter isalso erroneous.

If the object to be monitored is, for example, a vehicle, the stateparameter can, for example, be a driving situation of the vehicle,wherein the driving situation comprises, for example, a driving stateand a non-operated state.

A determination of a driving situation of a vehicle is of greatsignificance for a plurality of security-relevant aspects. In tirepressure monitoring, for example, a driver can always be informed aboutthe current pressure depending on the determined driving situation(state parameter), so that he can react immediately in case of apressure drop and can stop the vehicle, for example. Normally,battery-operated pressure sensors are used for measuring and monitoringthe tire pressure in a vehicle tire, which transmit their measurementvalues from the inside of the tire and preferably at the rim via atransmission unit to a central unit, for example a board computer,disposed outside the tire. Due to the required battery operation of thepressure sensor as well as the transmission unit, the life-span of suchsensor applications is limited. This problem, however, is not onlyencountered with the already mentioned tire pressure sensors where atime control for measurement and transmission is performed dependent onpressure or acceleration criteria, but also with any battery-operatedsensor systems, such as for separately positionable temperaturemeasurement devices.

Due to the life-span limited by battery operation, it is important tomake the decision with as few measurement cycles as possible. Sincefrequently decision certainties, which are to be higher than theaccuracy of an individual measurement with the sensor, are required fordecisions, normally, averages of a sequence of repeated measurements areused, or the measurements are taken more frequently than required andthen low-pass filtered. However, both approaches increase the powerconsumption, in the first case in proportion to a number of measurementrepetitions and in the second case in proportion to oversampling. At thesame time, decisions are to be made as early as possible when thecriteria are fulfilled, which results in a minimum frequency ofmeasurements and also a minimum bandwidth of low-passes for noisefiltering.

The tire pressure sensor arrangements used in the prior art formonitoring the tire pressure of a vehicle tire have a plurality ofdisadvantages. With the battery-operated tire pressure sensorconfiguration, it is not possible to take continuous measurements of thetire pressure measurement values over the whole life-span of the tirepressure sensor configuration, which is in the range of, for example, 10years. Common tire pressure sensor configurations have too high a powerconsumption for that, which limits the life-span of the battery-operatedtire pressure sensor configurations, so that a continuous measurement ofthe physical state parameters, such as pressure or temperature, can notbe performed with a sufficiently high measurement repetition rate duringthe whole intended life-span. A sufficient measurement repetition rateis determined by the time interval during which a change of the tirepressure is to be determined, so that the shorter the time intervalbetween the detection of the individual tire pressure measurement valuesand their transmission to an evaluation electronic, the higher thecertainty to detect a dangerous change of the tire pressure, whichindicates a critical state of the tire, soon enough.

Additionally, the power consumption of known tire pressure sensorconfigurations is determined by the associated sensor unit, which servesfor transmitting the individual tire pressure measurement values to thecentral unit, which performs the further processing of the transmittedtire pressure and tire temperature values, respectively. In the so farmost common tire pressure sensor configurations, the measurementfrequency for detecting the tire pressure measurement values and thetransfer frequency (abundance) for transmitting the tire pressuremeasurement values are adapted in dependence on the driving state of thevehicle detected via an additional acceleration sensor or an additionalmotion switch.

In order to detect pressure changes of the tire pressure, which indicatedamage of the tire, as soon as possible, in the tire pressure sensorconfigurations known in the prior art it is further required to performa significantly continuous measurement of the pressure and temperaturevalues in the tire in dependence on the detected driving state of thevehicle and transmit these to the central unit across a high-frequencyradio link. Thus, the relatively high turn-on frequency of thetransmission unit in the known tire pressure sensor configurations leadsto a relatively high average power consumption of the battery-operatedconfiguration, which has the consequence that the intended life-span of,for example, 10 years, cannot be achieved.

WO 03/080371 A2 describes, for example, a tire pressure monitoringsystem, where tire pressure measurement values, which are successive intime, are detected by a transmission unit for monitoring the tirepressure in a tire of a vehicle. At least part of the tire pressuremeasurement values is transmitted with a variable frequency to areceiver unit, wherein the frequency is derived from the detected tirepressure measurement values via a control unit.

The above-described approach according to the prior art utilizes thefact that dynamic load redistributions occur during a driving operationof the vehicle, which leads to a change of pressure in the tires. Forexample in a bend, the outer wheels are more heavily loaded andconsequently the pressure in these tires increases, while it decreasesin the relieved wheels on the inside of the bend. The same takes placeduring braking or accelerating between the wheels of the rear axle andthe front axle. Thereby, the transmission and measurement intervals ofthe tire pressure sensor system are determined by the measured tirepressure itself. For switching between a driving state and anon-operated state, switching thresholds are used, which are adaptedboth in the non-operated state and in the dynamical driving state, sothat, for example, static pressure conditions in the tire, as theyoccur, for example, during parking, and dynamic driving conditions arealways taken into consideration.

In the determination of the state parameter, such as the alreadymentioned driving situation of the vehicle, this is of particularimportance for battery-operated sensor systems where the measurementvalues are transmitted, for example, only in the driving state. Here, awrong decision for transmitting measurement data causes a strainingtransmission process with high current consumption, while a wrongdecision for not transmitting merely causes a short delay of thetransmission process.

If, for example, systems are used, which additionally use anacceleration sensor to determine the driving state of the vehicle, themeasurement rate and particularly the number of heavilycurrent-consuming RF transmissions can be reduced significantly in thenon-operated state compared to the driving state. However, theacceleration sensor has to be evaluated continuously in order todetermine when the driving state changes and thus the measurement andtransmission rates have to be changed. It applies for the frequency ofchecking the acceleration sensor that it has to be checked at least sofrequently that a time is kept, which is available for detecting thechange of the driving state.

In simple mechanical acceleration sensors where a mass is shiftedagainst, for example, a counter-force defined by a spring by theacceleration and closes a contact at a certain point of its path,monitoring this switch represents no significant current consumption,because a signal-noise ratio of the switching signal is so high that itcan be monitored continuously by a simple Schmitt trigger at the input.However, for reliability reasons, these switches are replaced bymicromechanical acceleration sensors, the signals of which often have tobe read out with the help of amplifiers and/or A/D converters. Here itapplies that an energy consumption of the evaluation circuit increaseswith increasing demands on accuracy. Examples for the causes are anextension of the measurement length for measurement repetition andaveraging, an increase of the sampling frequency and downstream low-passfiltering, an increase of current consumption for a more low-noise inputstage or an extension of the measurement time for a measurement valuewith an input circuit with lower bandwidth.

If, for example, gas pressure is monitored instead of the acceleration,the measurement data is further processed and transmitted from the tireto a receiver in the vehicle. However, a large part of the data is alsomeasured only for a derivation of decisions. For an accuracy with whichthis decision can be made, the same influences apply, which have beendescribed above for the acceleration sensor.

SUMMARY OF THE INVENTION

It is the object of the present invention to provide an improved conceptfor energy-efficient and reliable determination of a state parameter ofan object to be monitored.

In accordance with a first aspect, the inventive apparatus fordetermining a state parameter of an object to be monitored has a meansfor providing a plurality of measurement values, wherein the measurementvalues have information relating to the state parameter of the object tobe monitored, a comparison means for comparing the measurement valueswith a predeterminable comparison parameter, wherein the comparisonmeans is formed to output a first comparison signal when apredeterminable number of measurement values within a measurementinterval falls below the comparison parameter, or to output a secondcomparison signal when the predeterminable number of measurement valuesexceeds or reaches the comparison parameter, wherein the firstcomparison signal or the second comparison signal indicate the stateparameter.

In accordance with a second aspect, the present invention providesmethod for determining a state parameter of an object to be monitored,having the steps of: providing a plurality of measurement values,wherein the measurement values have information relating to the stateparameter of the object to be monitored; comparing the measurementvalues to a predeterminable comparison parameter to generate and outputa first comparison signal when a predeterminable number of measurementvalues within a measurement interval falls below the comparisonparameter or to generate and output a second comparison signal when thepredeterminable number of measurement values reaches or exceeds thecomparison parameter, wherein the first comparison signal or the secondcomparison signal indicate the state parameter.

In accordance with a third aspect, the present invention provides Acomputer program with a program code for performing the method fordetermining a state parameter of an object to be monitored, having thesteps of: providing a plurality of measurement values, wherein themeasurement values have information relating to the state parameter ofthe object to be monitored; comparing the measurement values to apredeterminable comparison parameter to generate and output a firstcomparison signal when a predeterminable number of measurement valueswithin a measurement interval falls below the comparison parameter or togenerate and output a second comparison signal when the predeterminablenumber of measurement values reaches or exceeds the comparisonparameter, wherein the first comparison signal or the second comparisonsignal indicate the state parameter, when the computer program runs on acomputer.

According to a further aspect, the present invention provides anapparatus for determining a driving situation of a vehicle, wherein thedriving situation comprises a non-operated state and a driving state ofthe vehicle, with a pressure sensor for detecting tire pressuremeasurement values, an evaluation means for evaluating a plurality oftire pressure measurement values to obtain a tire pressure-dependentdriving situation parameter, a means for determining a comparisonparameter from the tire pressure-dependent driving situation parameter,a means for providing the comparison parameter, wherein the means forproviding is coupled to the means for determining to obtain thecomparison parameter, a comparison means for comparing the tirepressure-dependent driving situation parameter with the comparisonparameter to determine the driving situation, wherein the means forproviding the comparison parameter is formed to provide the comparisonparameter to the comparison means and to maintain the comparisonparameter in successive determinations of the driving situation duringthe driving state.

The present invention is based on the knowledge that a state parametercan be determined in an energy-efficient and reliable way based on acomparison of measurement values with one or several comparisonparameters (thresholds), if a minimum number of measurement values,which are to fall below and exceed the predeterminable comparisonparameter, respectively, is determined or preset before, to make areliable decision about the state parameter and a change of the stateparameter, respectively.

If the state parameter is a driving situation of a vehicle, the stateparameter can, for example, indicate a non-operated state of the vehicleor a driving state of the vehicle. As has already been mentioned, thestate parameter is determined based on a comparison parameter.

The comparison parameter is preferably determined from the measurementvalues and can either be determined or adapted continuously, i.e. bothin the non-operated state and in the driving state, and also only duringthe non-operated state, wherein in the latter case a further reductionof the energy consumption of the inventive system results. A furtherreduction of the energy consumption results from the fact that accordingto the invention only as many comparisons are performed as areabsolutely necessary. If the state parameter determined in thenon-operated state is compared to the measurement values, it can bedetermined that the vehicle is in the non-operated state, for example,when the measurement values do not exceed the comparison parameter. Whenthe comparison parameter is exceeded, however, a dynamic driving stateis determined. In dependence on a degree of the exceeding a dynamic inthe driving state can be detected clearly, such as a slower drive or afast drive.

According to the invention, the comparison parameter can be used insuccessive determinations of the driving situation, particularly duringthe driving state. Preferably, no further adaption (tracking) of thecomparison parameter takes place. In a determined non-operated state ofthe vehicle, the comparison parameter can be adapted in order to detect,for example, statistical measurement variations during the parkingoperation, which are mainly determined by the noise of the sensor andthe circuits for evaluating the sensor.

Further, the inventive concept is based on the fact that the pressurechanges in a tire to be expected in a driving operation typically have adynamic of a few seconds due to a duration of typical drivingsituations. However, such pressure changes are not to be expected in theparking state (non-operated state), since the pressure in an intact tiregenerally varies only due to temperature changes and thus has a muchlower dynamic in a range of minutes or even hours. If the pressurechanges are suitably evaluated, a decision can be made without anacceleration sensor or another roll detector, about which situation(driving situation) the vehicle is in. The inventive comparisonparameter is “frozen” between the state of the quasi-static tire changesin a parked vehicle and the dynamic pressure changes in the drivingoperation, when a change to the dynamic state is made. Resetting intothe quasi-static state of operation is performed as a reverse of theopposite switching process, which means when the conditions for thedynamic state, which are monitored with the “frozen” threshold, are nolonger fulfilled.

The inventive approach has the advantage that the energy consumption isfurther reduced, since the comparison parameter is only determined inthe non-operated state and not continuously, i.e. both in the drivingoperation and the parking state. Thus, an adaption result is foreseeableand can be tested for its plausibility, since the result cannot beinfluenced by a traffic situation, road and weather conditions, thestyle of driving and/or the mood of the driver, the tire types and thevehicle weight as well as a chassis tuning. Additionally, a furtherreduction of the energy consumption and thus a further increase of thebattery life-span can be obtained, since the switching thresholds arenot adapted continuously, i.e. independent of a driving situation, suchas non-operated state or driving operation, but only in the parkingstate, which leads to a reduction of the energy consumption.

Due to the further reduction of the energy consumption of the inventivesystem, measurements of the tire pressure can be ensured over the wholelife-span of a tire pressure sensor system, e.g. in the range of 10years, with only one battery. This is due to the fact that a frequencyof pressure measurements as well as a time interval required forpressure measurement can be specifically influenced.

It is a further advantage of the present invention that no additionalacceleration sensor or motion switch has to be used for detecting thedriving state of the vehicle for detecting the driving situation, theevaluation of which leads again to an increased current consumption.

It is a further advantage of the present invention that data indicatingtire pressures can be transmitted regularly and with a minimumfrequency, e.g. hourly, to the central unit to allow monitoring of thefunctionality of the tire pressure sensor for the central unit. Theminimum frequency can further be adjusted adaptively so that the datatransmission only takes place when, for example, a significant pressurechange occurs.

It is a further advantage of the present invention that the switchingthreshold (the comparison parameter) is only adapted in the parkingstate. For that reason, the inventive switching threshold does notdepend on the driving dynamic of the vehicle, the style of driving ofthe driver, the road and route conditions or the type of tire or tirepressure, but changes merely in dependence on the noise present in astationary vehicle. This parameter can be easily predicted and dependsonly on switching properties, whereby a dimensioning of the system issignificantly eased, which will lead to cost reduction. Additionally,the inventive system is easier to test since the inventive switchingthreshold occurs also in a production test under normal environmentalpressure and can thus be measured again prior to delivery.

It is a further advantage of the present invention that merely oneswitching threshold (a comparison parameter) is used to differentiatebetween driving state and non-operated state. Apart from asimplification of a circuit complexity, it is achieved that theinventive switching threshold does not depend on individual drivingcharacteristics and vehicle types as well as tire types, but merely onthe characteristics of the sensor system which are known during theproduction of the sensor system and can thus be used for determiningplausibility checks, such as minimum and maximum limits of thecomparison parameter.

It is a further advantage of the present invention that a decision,which occurs rarely and which is to be made with high reliability, canbe derived from a relatively noisy signal without continuously having toperform an increased number of measurements for noise filtering orwithout having to set circuit parameters for decreasing the noise, suchthat, for example, an increased current consumption results. Further,the measurement intervals can be adapted to the maximum allowabledecision delays without considering boundary conditions, which the noiseof the measurement system dictates, and are only temporarily reduced fora few repetition measurements during exceeding a decision criterion dueto noise, which leads to a further reduction of the energy consumption.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and features of the present invention willbecome clear from the following description taken in conjunction withthe accompanying drawings, in which:

FIG. 1 is a basic block diagram of an inventive apparatus fordetermining a state parameter of an object to be monitored;

FIG. 2 is a basic circuit diagram of an inventive apparatus fordetermining a state parameter according to a further embodiment;

FIG. 3 is a basic circuit diagram of an apparatus for determining astate parameter according to a further embodiment;

FIG. 4 a-e are exemplary curves of the average tire pressure and ofparameters derived from the determined tire pressure, which are usedaccording to the invention for deriving a state parameter, which is adriving situation of a vehicle;

FIG. 5 is a basic block diagram for determining a state parameter of anobject to be monitored according to a further embodiment of the presentinvention;

FIG. 6 is a simulation image representing a derivation of the states“driving” or “non-operated”;

FIG. 7 a-c are exemplary representations of determined pressuremeasurement curves for determining a driving state; and

FIG. 8 is an exemplary representation of a determined pressuremeasurement curve for determining a driving state.

DETAILED DESCRIPTION OF THE INVENTION

The apparatus for determining a state parameter of an object to bemonitored illustrated in FIG. 1 comprises a means 101 for providing aplurality of measurement values, wherein the measurement values provideinformation relating to the state parameter of the object to bemonitored. The means 101 for providing has an output coupled to an inputof a comparison means 103. Further, the comparison means 103 has afurther input 105, to which a comparison parameter can be applied, aswell as an output 106 for providing a first comparison signal and/or asecond comparison signal.

The comparison means illustrated in FIG. 1 is formed to compare themeasurement values provided by the means 101 for providing with apredeterminable comparison parameter. Thereby, the means for comparing103 is formed to output a first comparison signal when a predeterminablenumber of measurement values within one measurement interval falls belowthe comparison parameter, or to output a second comparison signal whenthe predeterminable number of measurement values exceeds or reaches thecomparison parameter, wherein the first comparison signal or the secondcomparison signal indicate the state parameter.

The means 101 for providing the plurality of measurement value comprisesa sensor means, such as a tire pressure sensor for providing tirepressure measurement values or an acceleration sensor for providingacceleration measurement values, wherein the tire pressure measurementvalues or the acceleration measurement values can be the measurementvalues.

In the following, for the purpose of simplifying the specification, itis assumed that the measurement values can be tire pressure measurementvalues. Here, it should be noted, that the measurement values can alsobe acceleration measurement values or other measurement values, such asthe temperature of the gas filling of the tire, the chemical compositionof the gas filling, etc., which are obtained via a temperature sensor, achemosensor, etc.

According to a further aspect, the inventive means 101 for providing themeasurement values comprises an evaluation means for evaluating theplurality of tire pressure measurement values to provide evaluatedmeasurement values.

According to a further embodiment, for determining the evaluatedmeasuring values, the inventive evaluation means comprises a means fordetermining an average value of the plurality of measurement values aswell as a subtracter for determining a difference between themeasurement values and the average value, wherein the evaluatedmeasurement values are the difference or an amount of the difference.The means for determining the average value can, for example, have alow-pass filter to determine the average value by low-pass filtering.

According to a further embodiment, the evaluated measurement values canbe determined merely from a difference between successive measurementvalues. In that case, the inventive evaluation means comprises asubtracter for determining a difference between successive measurementvalues, wherein the evaluated measurement values are the difference oran amount of the difference.

According to a further embodiment, the inventive evaluation meanscomprises a squaring means for squaring the above-mentioned differenceor an amount of the difference to obtain a squared difference, whereinthe evaluated measurement values are the squared difference.

The comparison means 103 receives the plurality of measurement values ora plurality of processed measurement values or both from the means 101.

According to a further aspect, the inventive apparatus for determiningthe state parameter comprises a means for determining a predeterminablecomparison parameter, wherein the means for determining is formed toprovide the predeterminable comparison parameter to the comparison means103.

The means for determining the comparison parameter is, for example,formed to determine an average value of the evaluated measurementvalues, wherein the average value of the evaluated measurement value isthe predeterminable comparison parameter. For determining the averagevalue, the means for determining the comparison parameter comprises, forexample, a low-pass filter to determine the average value of themeasurement values by low-pass filtering the same. The cutoff frequencyof the filter for determining the comparison parameter can differ fromthe cutoff frequency of the filter for processing the measurement valuesin the means for providing the measurement values. Typically, the cutofffrequency of the filter for determining the comparison parameter islower.

Additionally, the inventive means for determining the comparisonparameter can be formed to output a plurality of the comparisonparameter or a fraction of the comparison parameter as thepredeterminable comparison parameter. Thereby, for example, an averagevalue of the measurement values (and the processed measurement values,respectively) is multiplied by a factor so that plurality of the averagevalue is provided to the comparison means 103 as comparison parameter.Analogously, the inventive means for determining a comparison parametercan be formed to output a fraction of the determined comparisonparameter as the comparison parameter. Thereby, for example, thedetermined average value of the measurement values is evaluated with afactor in a multiplicative way, wherein the factor is smaller than 1. Inthat way, by staggering the plurality as well as the fractions of thepredeterminable comparison parameters, which are defined as switchingborders, additional states can be defined, such as non-operated state,driving state with low dynamic, driving state with high dynamic andalarm state, for example in an unexpectedly high pressure drop.

According to the invention, the comparison means 103 is formed to usethe comparison parameter, which is determined, for example, in anon-operated state of a vehicle, in successive determinations of thedriving situation during the driving state. To obtain a further powerconsumption reduction, according to the invention, the comparisonparameter is only determined when, for example, the first comparisonsignal indicates the non-operated state. Thus, the inventive means fordetermining the comparison parameter can be controllable so that thecomparison parameter is preferably only determined if, for example, thenon-operated state has been determined, and that an adaption of thecomparison parameter is interrupted if, for example, the secondcomparison signal indicates the driving state. According to theinvention, a control means is used for controlling the means fordetermining the comparison parameter, which is formed to generate afirst control signal in response to which the means for determining thecomparison parameter determines the comparison parameter and to generatea second control signal in response to which the means 109 fordetermining the comparison parameter interrupts a determination, i.e. anadaption, of the comparison parameter.

Preferably, the inventive control means is formed to derive the firstcontrol signal and the second control signal from the first or from thesecond comparison signal. If, for example, the first comparison signalindicates a non-operated state, and the second comparison signal, forexample, a driving state, the first control signal is generated, forexample, when a non-operated state is indicated. Analogously, the secondcontrol signal is generated when the driving state is indicated.Basically, the control means is formed to output the first controlsignal when the first and/or the second comparison signal indicates thenon-operated state and to output the second control signal when thefirst and/or the second comparison signal indicates the driving state,since the driving state to be indicated can be associated to the firstor to the second comparison signal. For example, when the second controlsignal (driving state) occurs, the adaption of the comparison parametercan be terminated while it will be performed when the first controlsignal (parking state) is present.

According to a further embodiment, the means for determining thecomparison parameter can also be controlled directly based on the firstcomparison signal or the second comparison signal. Therefore, forexample, the output 106 of the comparison means can be coupled back tothe means for determining the comparison parameter to control itsoperation.

According to a further embodiment of the present invention, the means101 for providing a plurality of measurement values comprises ameasurement sensor, wherein the measurement sensor is, for example, atire pressure sensor or a acceleration sensor. For the case that thestate parameter is a driving situation of the vehicle, comprising anon-operated state and a driving state, the inventive measurement sensorhas a first measurement rate in the non-operated state and a secondmeasurement rate in the driving state, wherein the first measurementrate and the second measurement rate differ. Since, for example, in anon-operated state the pressure changes are lower than in a drivingstate, the first measurement rate is preferably lower than the secondmeasurement rate, whereby a further reduction of the energy consumptionis obtained. Thus, in the non-operated state, a time interval betweentwo successive measurements can be, for example, in a range between 1second and 10 seconds. In comparison, the measurement rate is increasedin the driving state, so that the second measurement rate is, forexample, in a range of 0.1 seconds to 1 second.

Controlling the pressure sensor with regard to the measurement rate can,for example, be performed in dependence on the respectively indicateddriving state. The inventive apparatus for determining the stateparameter can therefore, for example, have a further control means,which is formed to derive a pressure sensor control signal from thefirst comparison signal or the second comparison signal, based on whichthe respective measurement rate is set.

Additionally, the inventive apparatus for determining the stateparameter can have a transmitter for transmitting the first comparisonsignal and/or the second comparison signal, for example to a centralunit disposed in the vehicle, which informs the driver about the currentpressure curve, for example based on the received first and/or secondcomparison signal. The transmitter can, for example, be a radiotransmitter, so that communication between the inventive apparatus fordetermining the driving situation and the central unit can be performedwireless.

According to the invention, the gas pressure in the tires can bemeasured in time intervals, which are, for example, shorter than thetime interval aimed at for detecting the transition between, forexample, a non-operated state and a driving state. From the successivepressure measurements, an average value of the pressure curve is formedby filtering. The average value can, for example, be a short-termaverage value, indicated by the fact that only a few pressuremeasurement values are used for its determination. A difference to theaverage value is formed from every measurement value, wherein thedifferences are then squared. According to the invention, the squares ofthe differences are again filtered to determine an average value of thesquared deviations. The average value of the squared deviations canagain be a short-term average value. The cutoff frequency of the filterfor determining the average value of the squared deviations can differfrom the cutoff frequency of the filter for determining the averagevalue of the pressure measurement values for the difference formation.Typically, the cutoff frequency of the filter for determining theaverage value of the squares deviation, which is used as comparisonparameter, is lower.

There is, for example, a transition from an operated state to a drivingstate when a predetermined number of exceedings of the currentdifference square over a predetermined multiple of the short-termaverage values of the difference of the squares, e.g. 5, occurs within apredetermined number of measurements. In this transition, filtering ofthe difference squares is terminated and the last short-term averagevalue of the difference squares is maintained as comparison parameter.There is, however, a change from a driving state to a non-operated statewhen the switching condition from the non-operated state to the drivingstate is not fulfilled within a predetermined number of measurements.After switching back to the non-operated state, filtering of thedifference squares to an adaption of the switching threshold (comparisonparameter) is activated again. Thereby, the fact that the switching andenvironment parameters influencing the adaption behavior do notsignificantly change in a parking operation is utilized, so that for along time, for example, the same pressure sensor is used, whereby asensor-typical plausibility check becomes possible. The predeterminednumber of measurements for switching from the parking state to thedriving state and vice versa are not necessary equal. Typically, thenumber of measurements for switching from the driving state to theparking state is significantly higher than the number of measurementsfor switching from the parking state to the driving state.

According to a further embodiment, in addition to the current tirepressure, further information can be provided, which can only becalculated when measurements are taken in constant time intervals.Examples therefor are low-pass filtered pressure values or movingaverage values, a deviation of the measurement from the previous valueor a low-pass filtered or averaged value or measured values forgradients of variations of the measurement values across a monitoringtime interval of, for example, one minute.

According to the invention, the measurement times in the driving statecan differ from the ones in the non-operated state. As has already beenmentioned, this can be easily controlled because an adaption of theswitching thresholds (comparison parameter) is only performed in one ofthe two states. As has already been mentioned, the pressure differencecan be obtained directly from two successive pressure measurements,without having to form an average value (for example a short-termaverage value). Analogously, instead of the difference squares,difference amounts can be used, which are output as the first comparisonsignal or the second comparison signal. The multiple of the short-termaverage value is, for example, limited by a maximum value to ensure thathigh pressure deviations, which are not plausible in a non-operatedstate, always lead to a transition to the driving state. The multiple ofthe short-term average value is, for example, limited by a minimum valueto ensure that pressure deviations which are clearly too low for adriving state can not lead to an unnecessary transition to the drivingstate. The frozen value of the short-term average value and thedifference squares (comparison parameter) is adapted to theproportionality of the thermal noise by temperature compensation. Thethermal noise is the significant portion that can cause measurementdifferences in the non-operated state. The temperature compensation isthereby adapted to the absolute temperature. This means that in atemperature rise the switching threshold (comparison parameter) that isdefined by the transition from the non-operated state to the drivingstate, is also increased to make the switching condition independent ofthe temperature.

If the state parameter is, for example, the already mentioned drivingsituation of a vehicle, which comprises a non-operated state and adriving state, it has already been mentioned that the predeterminablecomparison parameter is preferably determined or substantially usedmainly in the non-operated state in order to save energy. According to afurther aspect, the inventive apparatus for determining the stateparameter comprises a means for providing the predeterminable comparisonparameter, which is used as interface between the means for determiningthe comparison parameter and the comparison means. Thereby, the meansfor providing is formed to maintain the predeterminable comparisonparameter (comparison parameter) at the current value of the same, whenthe first comparison signal or the second comparison signal indicates atransition between the non-operated state and the driving state. Thatway, it can be ensured that, for example in a deactivation of the meansfor determining the comparison parameter the same will not get lost.

In order to make a decision about the first comparison signal or thesecond comparison signal, the inventive comparison means is formed toperform a plurality of comparisons within the measurement interval,wherein the first comparison signal is generated when thepredeterminable number of measurement value within the measurementinterval falls below the comparison parameter, and wherein the secondcomparison signal is generated by the comparison means when thepredeterminable number of measurement values reaches or exceeds thecomparison parameter. Thus, the measurement interval is determined by ameasurement number, i.e. by the plurality of measurement values withinthe measurement interval.

According to a further aspect, the inventive apparatus for determining astate parameter comprises a means for determining the number ofmeasurement values. The means for determining the number of measurementvalues is, for example, formed to determine the number of measurementvalues by using a maximum allowable error probability, wherein themaximum allowable error probability indicates a maximum allowableprobability of a wrong decision about the first comparison signal orabout the second comparison signal from the plurality of comparisons,wherein the plurality of comparisons is equal to or smaller than thenumber of measurement values. Preferably, the means for determining thenumber of measurement values is formed to determine the number ofmeasurement values n by using the following equation:n=log(p _(el))/log(p _(emax)),

wherein log(p_(el)) is the logarithm of an error probability p_(el) of ameasurement value, and wherein log(p_(emax)) is the logarithm of themaximum allowable error probability p_(emax).

Here, use is made of the fact that the signal of, for example, apressure or an acceleration sensor in the tire of a parked vehicle issubject to merely very low variations by a change of temperature and thenoise of the measurement configuration caused by the system. In mostcases, it can be assumed for the noise that it is a band-limited whitenoise. The measurement rates in the systems will always be in the rangeof several Hertz (Hz) due to the requirement to save energy, wherein thebandwidth of the white noise can be expected to be many powers of tenhigher. In this constellation, the noise is heavily subsampled andalmost the whole noise energy lies in frequency ranges far above theNyquist frequency of the sampling system. Under these conditions, twosuccessive measurements can be considered as uncorrelated in goodapproximation.

In this case, it holds true that the probability of multiple randomexceedings of a threshold, i.e. for example the (wrong) detection of adriving state although the vehicle is still parked is equal to theproduct of the individual probabilities for uncorrelated random events.If the system is dimensioned such that the switching threshold(comparison parameter) is at several multiples of the standarddeviation, a probability of 0.3% results that a measurement value willtrigger a wrong decision because it falls across the threshold due tothe noise, for example, for a switching threshold at three times astandard deviation by assuming a Gaussian random process. Theprobability that this happens three times in a row is at, for example,(0.3%)^3=27 ppm based on the assumption that the individual measurementsare uncorrelated.

The inventive system has a switching threshold (comparison parameter),during the undershooting and exceeding of which an action is triggered,such as the transmission of measurement data towards the outside or achange of a system-internal state, which again results in an increase ofthe sampling rate. This switching threshold can be determined adaptivelyor can be altered by a timer in a time-dependent way. The noise causedby the sensor system, which comprises, for example, the pressure sensor,and its characteristic are known, which results in an error probability(p_(el)) for the individual measurement. In order to make a decisionwith the predetermined maximum allowable error probability (p_(emax)), arepetition number is calculated, which results as a rounded-up integerquotient of the logarithm of the two error probabilities. The repetitionnumber is a number of the comparison repetitions, which is predeterminedby the already mentioned number of measurement values. If a decisioncriterion is fulfilled, a decision is repeated. If the decision is notthe same in the repetition, the decision is discarded and repetitionsare terminated. If the decision is the same in the repetition, therepetition is continued until n repetitions with the same result arepresent, and only then the decision about the state parameter is finallymade. The error probability for the n-fold decision is then:p _(e(m of n)) =p _(el) ^(n).

The repetitions are only made when a decision, e.g. a change from theparking state to the driving state in the case of a tire pressuresensor, would be made due to an individual decision attempt. If thisattempt already indicates that probably no decision will be made,repetitions can be abandoned and the energy consumption-intensivefurther measurements can be saved.

However, not all repetitions have to turn out the same for the decisionto be made, but, according to the invention, a rate is defined and thevalue ‘m’ from n decision attempts has to be positive. Thereby, thevalue ‘n’ is, for example, the number of measurement values within themeasurement interval and the value ‘m’ the predeterminable number ofmeasurement values. The error probability then results as:p _(e(m of n)) =p _(el) ^(n)/(1−p _(el))^(m-n).

This variation is particularly useful when the signal to be decided onis also random and can occasionally fall to a value which would not leadto a decision. For example, the decision whether a vehicle is driving ornot can turn out wrong again and again due to short stoppinginterruptions although the vehicle has not been parked again, due to thetire pressure or due to a measurement of the centrifugal force with anacceleration sensor, even when the vehicle has already started driving.In this context, parking means a longer parking of the vehicle.

However, according to the invention, several thresholds can be defined,which have to occur with a different frequency to lead to a decision.For example, a first threshold has to occur ten times in a threefoldstandard deviation, a second threshold five times in a fourfold standarddeviation, a third threshold two times in a fivefold standard deviationand the decision is only finally made when one of the criteriaassociated to the different switching thresholds is fulfilled within adefined time window.

According to the invention, however, different thresholds can beintroduced, wherein points are associated to every threshold. Thereby,for example, a first threshold provides one point in a threefoldstandard deviation, a second threshold two points in a fourfold standarddeviation, a third threshold four points in a fivefold standarddeviation. The points are added up over a defined time window and thedecision is only really made when a defined minimum number of points isobtained.

The time intervals of the repetition measurements do not have to bewithin the same period as the measurements prior to the thresholdexceeding, but can be performed faster to ensure a sampling rate whichis, on the one hand, still significantly below the bandwidth of thesuperposed noise but, on the other hand, possibly oversamples signals tobe detected, e.g. driving-induced pressure changes, i.e. faster than theNyquist rate defined by the Shannon sampling theory. If the repetitioncriterion is not fulfilled, a transition back to the old sampling ratedefined for the parking state is made. When the repetition criterion isfulfilled, the increased sampling rate can be maintained or a transitionto another sampling rate defined for the driving state can be made.

According to a further aspect, the inventive apparatus for determiningthe state parameter comprises a means for determining thepredeterminable number. The means for determining the predeterminablenumber is preferably formed to determine the predeterminable number independence on a standard deviation of the measurement values, as hasalready been described.

The predeterminable number comprises, for example, a firstpredeterminable number and a second predeterminable number, wherein themeans for determining from the predeterminable number is formed todetermine the first predeterminable number in dependence on a firststandard deviation of the measurement values, and to determine thesecond predeterminable number in dependence on a second standarddeviation of the measurement values, wherein a first weighting point isassociated to the first standard deviation, and wherein a secondweighting point is associated to the second standard deviation, as hasalready been described. The inventive comparison means is formed toperform a plurality of comparisons, wherein the first or the secondweighting point is associated to every comparison, and to generate thefirst comparison signal or the second comparison signal based on the sumof the weighting points, as has already been mentioned. Preferably, thefirst comparison parameter indicates the non-operated state of thevehicle, while the second comparison parameter indicates the drivingstate of the vehicle. This applies to the case where the state parameteris a driving situation of the vehicle comprising the non-operated stateand the driving state.

In FIG. 2, a circuit diagram of an inventive apparatus for determining astate parameter of an object to be monitored according to a furtherembodiment is illustrated.

The apparatus comprises a sensor 201 coupled to a band-pass filter 203.An output signal of the band-pass filter 203 is branched, wherein bothportions are supplied to a multiplier 205. The multiplier 205 has anoutput 207, which is coupled to a first input 209 of a processing means211, which can be a processor. Further, the processing means 211comprises a second input 213, a first output 215 as well as a secondoutput 217.

Further, the output 207 of the multiplier 205 is coupled to a firstinput 219 of a low-pass filter 221. Further, the low-pass filter has asecond input 223 coupled to the first output 215 of the processing means211.

The pressure sensor 201 (sensor) is formed to acquire tire pressuremeasurement data and to supply the tire pressure measurement value tothe band-pass filter 203. Then, the pressure signal (tire pressuremeasurement value) is band-pass filtered to filter out the frequencyrange in which changes of the tire pressure caused by the drivingoperation are expected, as much as possible from the higher-frequencynoise and the lower-frequency pressure changes caused by the ambienttemperature. The output signal of the band-pass filter is then squaredwith the aid of the multiplier 205. The squared output signal of theband-pass represents a measure for a current size of the pressurechanges in the relevant frequency range and will be referred to asshort-term variance measure below. The squared signal is again low-passfiltered in the parking state (static) to obtain a long-term averagevalue of the short-term variance measure. In the following, this valueis referred to as long-term variance measure.

In the driving state (dynamic), the low-pass filtering is interruptedand the long-term variance measure remains constant on the last valueprior to the change to the value determined in the parking operation orone of the immediately subsequent values.

Thereby, the processing means 211 takes on the task to make a decisionabout a transition from parking operation to driving operation and viceversa. Thereby, the processing means 211 has, for example, aconfiguration as basically illustrated in FIG. 3.

A possible realization of the processing means 211 illustrated in FIG. 2is shown in FIG. 3. First, the processing means comprises threeamplifiers 301, the inputs of which are coupled to the second input 213.The outputs of the amplifiers 301 are each connected to the first inputof a respective subtracter 303. The first input 209, however, is coupledto the respective second input of the respective subtracter 303. Each ofthe subtracters 303 has an output which is coupled to a sign decisionmeans 305 as well as a restrictor 307 with an amplifier 309. Each of theamplifiers 309 has an output, wherein the outputs of the amplifiers 309are provided to a summator 311. The summator 311 has an output 313coupled to a first input of an integrator 315. The integrator has twooutputs, wherein the first output of the integrator is coupled to arestrictor 317. The restrictor 317 has an output 319 coupled to a delaymember 321. Further, the output 319 is coupled an AND operation block323. The AND operation block 323 has a further input, which is coupledto an output of a step counter 325. Further, the AND operation block 323has an output coupled to an S input of an S-R flip-flop 327. Theflip-flop 327 has two outputs, which are coupled to the outputs 215 and217 of the processing means 211.

An output of the delay member 321 is coupled to an OR operation block329. An output of the OR operation block 329 is connected to the secondinput of the integrator 315. Further, the OR operation block 329 has afurther input coupled to an output of a delay member 331. The delaymember 331 has an input coupled to an output of a restrictor 317. Therestrictor 317 comprises an input coupled to an output of an integrator333. A first input of the integrator 333 is connected to a block 335 forproviding a constant. A second input of the integrator 333 is connectedto the second input of the integrator 315 and to the output of the ORoperation block 329.

The output of the delay member 321 is coupled to an input of an ORoperation member 335. The OR operation member 335 has an output coupledto a second input of an integrator 337. A first input of the integrator337 is coupled to a block 339 for providing a constant value. Theintegrator 337 has an output coupled to the input of a restrictor 317.The restrictor 317 has an output coupled to an output of a delay member341. The delay member 341 has an output coupled to a second output ofthe OR operation member 335. Further, the output of the delay member 341is connected to an R input of the flip-flop 327.

Further, a signal tap area 343 is illustrated in FIG. 3, via which asignal applied to the output of the summator 311 can be tapped.Additionally, a tap area 345 is illustrated in FIG. 3, via which anoutput signal of the AND operation block 323 can be tapped. Further,FIG. 3 shows a tap area 347, via which an output signal of the delaymember 341 can be tapped.

The processing means illustrated in FIG. 3 is formed to perform adecision about a transition from the parking operation to the drivingoperation preferably according to the method discussed below.

When the short-term variance measure (delta) exceeds a defined multipleof the long-term variance measure (delta_AV), one counter isincremented. As a variation illustrated in FIG. 3, several multiples(e.g. eightfold, sixteenfold and thirty-twofold) can be defined, and, ata higher multiple, the counter is incremented immediately by severalsteps, such as 1, 2 and 4. When the counter, which is realized by theintegrator 315, reaches or exceeds a threshold within a defined timewindow generated by the integrator 333, a signal is generated, which canbe tapped via the tapping area 345. If the threshold (comparisonparameter) is not reached when the time window ends, the counter isreset. When the above-mentioned signals occurs in the parking state, atransition to the driving state is made, which is performed by theflip-flop 327. When the above signal does not occur at least once in thedriving state within a further time window defined by the integrator337, a transition back to the parking state is made, which can becontrolled via the signal applied to the tapping area 347.

Exemplary simulation examples of the average tire pressure areillustrated in FIGS. 4 a-e, which illustrate a derivation of the statesdriving or non-operation by the method described below.

Pressure measurement values are illustrated in FIG. 4 a, wherein thepressure has been measured exemplarily in an 0.5 second interval.Starting from the pressure measurement values, a short-term averagevalue is calculated, which is illustrated in FIG. 4 b. For calculatingthe short-term average value, a first-order IIR filter has been used,which has the following transmission function:

${H_{{IIR}\; 1}(z)} = {\left( \frac{1 - a}{1 - {a \cdot z^{- 1}}} \right).}$

Here, the term ‘a’ indicates a constant determining the cutoff frequencyof the filter.

In FIG. 4 c, a difference of the pressure values to the short-termaverage value of the pressure measurement is shown. This has beengenerated by a high-pass filtering(H _(HP)=1−H _(IIR1)(z)).

In order to reduce the noise influence, a band-pass filter can be usedinstead, which attenuates again the highest present portions of thesignal above the frequency generated by the driving motions of thevehicle. Further, the differences are squared, which results in ashort-term variance measure illustrated in FIG. 4 d by the referencenumber (401).

The difference squares are again filtered with an IIR filter, which hasthe following transmission function:

${{H_{{IIR}\; 2}(z)} = \left( \frac{1 - b}{1 - {b \cdot z^{- 1}}} \right)},$

wherein ‘b’ indicates a constant determining the cutoff frequency of thefilter.

In the considered embodiment, the vehicle is first parked and begins todrive after 600 seconds. This leads to a change of state (curve 402)after the above-mentioned signal illustrated in FIG. 4 e has beengenerated in the above-described method. The long-term variance measureis acquired starting from the transition to the driving state. Thevehicle drives for about two hours and is parked again after about 7500seconds, which can be seen in FIG. 4 e (curve 403). After a defined timewindow has passed, within which no signal has occurred, a further signald2 s is generated, which causes a transition back to the parking state(curve 405).

Alternatively, the value via the input signal to the squaring meansgenerating the short-term variance measure, can also be generated by amore complex band-pass, which has, for example, the followingtransmission function:

${H\; b\; p\; 3_{2}(z)}:={\left\lbrack {1 - \left\lbrack \frac{\frac{1}{16}}{1 - {z \cdot \left( {1 - \frac{1}{16}} \right)}} \right\rbrack} \right\rbrack \cdot \left\lbrack {\sum\limits_{v = 0}^{N - 1}\left( {b_{v} \cdot z^{- v}} \right)} \right\rbrack \cdot \frac{1}{6}}$with $b:=\begin{pmatrix}1 \\2 \\2 \\1\end{pmatrix}$

From the above discussion it becomes clear that further, according tothe invention, a time interval for transmitting the measurement valuesof the tire pressure sensor is determined such that the tire pressuresensor system can be operated by one battery over its whole life-span.Thereby, no measurement with an acceleration sensor is required todetermine when non-operated periods occur, where the transmission ratecan be reduced significantly in order to save energy.

The inventive system shows a behavior comparable to already existingsolutions with acceleration sensors, so that it can replace the same. Incontrary to the known methods, the adaptivity is improved by adaptingonly when low static variations of the tire pressure occur, such as in aparked vehicle. This provides the advantage that the behavior is onlyinfluenced by the noise of the pressure sensor system and by changes ofthe temperature, since tires can be seen approximately as isochoresystems. The influences of temperature are so slow that they can beseparated from the noise by simple filtering and thus they represent noreal interference. The noise is mainly dependent on typical circuitproperties, e.g. overall capacity of a capacitive pressure sensor,resistance of a resistive pressure measurement bridge, input noise andquantizing noise of an analog/digital converter, and can thus bepredicted easily.

According to the invention, it is avoided by simple comparisons that theadaption, which is to substantially eliminate the temperature dependenceand production deviation of the system parameters, drifts off toimplausible ranges due to unfavorable conditions in the drivingoperation. Further, in the inventive concept, less parameters arerequired and the hardware and software effort is reduced, whereby boththe system cost and the current consumption determining the life-span inbattery-operated systems can be reduced.

FIG. 5 shows a block diagram of an inventive apparatus for determining astate parameter for the case that the state parameter is a drivingsituation of a vehicle determined based on tire pressure measurementvalues.

The apparatus indicated in FIG. 5 comprises a pressure sensor 501coupled to an evaluation means 503. The evaluation means 503 comprisesan output 505 to which a comparison means 507 as well as a means 509 fordetermining a comparison parameter are coupled. The comparison means 507has a further input 511 as well as an output 513. The means 509 fordetermining the comparison parameter has an output, which is coupled toa means 514 for providing the comparison parameter. The means 514 forproviding the comparison parameter has an output, which is coupled tothe further input 511 of the comparison means.

The pressure sensor 501 is formed to measure the tire pressure and totransmit the tire pressure measurement values to the evaluation means103. The evaluation means 503 is formed to evaluate a plurality of tirepressure measurement values provided by the pressure sensor 501 tooutput evaluated measurement values as the measurement values via theoutput 505. The evaluation means 503 corresponds to the alreadydescribed evaluation means for evaluating the plurality of measurementvalues.

The means 509 for determining the comparison parameter is formed toreceive the measurement values to determine therefrom the comparisonparameter and to provide the comparison parameter (the predeterminablecomparison parameter) to the means 514 for providing the comparisonparameter. The means 514 for providing the comparison parameter isformed to provide the comparison parameter to the comparison means 507.

The comparison means 507 is formed to compare the measurement valueswith the comparison parameter to determine the driving situation.Thereby, the comparison parameter is used, as has already beenmentioned, in successive determinations of the driving situation, e.g.during the driving state of the vehicle. According to the invention, thecomparison parameter, which is provided by the means 114 for providingthe comparison parameter 107, is maintained for a number of comparisonprocesses after the driving state has been determined. Thereby, thecomparison means 507 can, for example, store the previously determinedcomparison parameter so that the same can be used until the nextindicated non-operated state.

The means 514 for providing the comparison parameter can, for example,comprise a memory where the comparison parameter determined in theparking state is stored and can be used and provided, respectively, forthe comparison in the driving state. Additionally, the means 514 forproviding the comparison parameter can, for example, be an interface ora connection between the means 509 for determining the comparisonparameter and the comparison means 507 to apply the determinedcomparison parameter to the input of the comparison means 507. In thatcase, the means for determining the comparison parameter can determinethe same both in the parking state and in the driving state.

The means 514 for providing the comparison parameter can further beformed to maintain the comparison parameter on its current value when achange of the determined driving situation between the non-operatedstate and the driving state occurs.

Further, it should become clear that the means 514 for providing can beformed separately and can be associated to the comparison means 507 andthe means 509 for determining, respectively.

The comparison means 507 is formed to determine the driving situationbased on the comparison between the measurement values provided by theevaluation means 503 and the comparison parameter. Preferably, thecomparison means 507 is formed to output the first comparison signal orthe second comparison signal, which indicates the driving situation(state parameter), for example the non-operated state or the drivingstate.

The comparison means 507 is formed to output, for example, the firstcomparison signal, which indicates the non-operated state of the vehiclewhen the predeterminable number, for example 2, of the measurementvalues falls below the comparison parameter and does not exceed thesame, respectively.

Analogously, the comparison means 507 is formed to output the secondcomparison signal, which indicates the driving state of the vehicle whenthe predeterminable number, such as 2 or more, of measurement valuesexceeds the comparison parameter or does not fall below the same.Thereby, the fact is utilized that the measurement values exceed theaverage value of the measurement values determined in the parking statedue to the higher dynamic in the driving state compared to the parkingstate.

However, according to the invention, for example, a grading of thestates can also be detected. If, for example, the driving state has afirst driving state with a first dynamic and a second driving state witha second dynamic, the comparison means 507 according to a furtherembodiment is formed to output the first comparison signal indicatingthe first driving state when a number of measurement values exceeds thefirst multiple of the comparison parameter but does not exceed or fallbelow a second multiple. Analogously, the second comparison signalindicates that the second driving state is predominant when the number(for example 2 or 3) of the measurement values exceeds the secondmultiple, for example fivefold, of the comparison parameter. Thisgrading applies particularly when the second dynamic is larger than thefirst dynamic, i.e. when the second driving state is, for example,characterized by a higher speed than the first driving state.

FIG. 6 illustrates a derivation of the states “driving or non-operated”,wherein for the derivation of the states the method described below isused exemplarily. The samples 601 illustrate the squared high-pass orband-pass filtered pressure values. It is typical of these values thatthey are lower in the parked vehicle than in the driving vehicle,because pressure variations due to the different load of individualtires are added to the noise of the measurement values during driving.At the beginning of the shown measurement, the vehicle was parked and itcan be seen that only a few samples exceed the drawn threshold due tothe noise of the individual measurement values, wherein these samplesare indicated by ‘a’. If this occurs, the measurement is repeated. Sincethe vehicle is still parked, the measurement variations only occur dueto the mainly thermal noise, which is caused by the sensor and themeasurement circuit and thus they contain high power density portions inhigh frequencies. In the samples indicated by ‘a’, it will be determinedwith high probability in the repetition that the value of therepetitions measurement lies below the value of the threshold. Due tothe fact that the threshold exceeding will not be repeated with highprobability, it can be assumed that it has occurred due to measurementnoise. As has been described above, a certain number of repetitions ofcriteria fulfillment within a window of a predetermined number ofmeasurement values is predetermined (n of m) in order to trigger a statechange. In a random exceeding of the switching threshold due to noise,this will not occur with high probability. As a result of this, nofurther action will be initiated. When reaching the point indicated with‘b’, the vehicle starts driving. The threshold is again exceeded. Then,the measurement is repeated again. The pressure variations due to whichthis exceeding has occurred are band-limited. This means that exceedingthe threshold can be reproduced in consecutive measurements with highprobability and, therefore, the criterion for multiple exceeding withinthe time window for the predetermined number of measurement values willbe fulfilled. This leads to a transition to the driving state.

FIGS. 7 a-c show exemplary representations of determined pressuremeasurement curves for determining a driving state based on furtherembodiments.

The exemplary diagrams illustrated in FIGS. 7 a-c are based on pressuremeasurements in a tire during a driving test. The test begins and endswith 600 seconds parking each and contains in between two hours drivingtime in city traffic. In FIG. 7 a, the pressure curve 701 and itsaverage value 703 obtained by low-pass filtering are illustrated.

In FIG. 7 b, the pressure curve values are high-pass filtered (in thiscase by a difference formation of measurement value and average value).For this, other high-pass or band-pass filters can be used. The valuesillustrated in FIG. 7 c correspond to the squares of the differencesshown in FIG. 7 b. The curve 707 shown in FIG. 7 c illustrates a fallingthreshold and in the illustrated case the pulse response of an IIRfilter. When the curve 707 intersects the curve 705, a pressuremeasurement value is transmitted. It can be seen that during parkingtimes (here 600 seconds at the beginning and the end) this can only bedone at very large time intervals.

As a variation, the measurement can be performed with lower resolutionand can thus be performed with simpler and more current-saving circuitsand methods.

In FIG. 8, the results of an increase of noise of the measurementcircuit or the pressure sensor are illustrated, which substantially havean effect on the signal voltages while the vehicle is parked, since theoverlaying pressure signals during driving are higher and drown out thisnoise. Therefore, premature exceedings of the dynamic threshold will beallowed due to increased noise. If this occurs, the decision is againverified by repetitions in the same way as has already been described.The positions indicated by ‘a’ mark threshold exceedings, which are notverified by repetitions since they occur due to high-frequency noise.The positions indicated by ‘b’ mark threshold exceedings which areverified by repetition because they are caused by pressure changes inthe tire due to driving dynamic (e.g. load change during braking ordriving in bends), which change only slowly compared to noise.

Further, the fact can be used that wrong decisions for making a decisioncan be given other error tolerances than for not making a decision. If,for example, a tire pressure sensor is to be switched from the parkingstate to the driving state, a wrong switching from the parking state tothe driving state has much more serious effects, namely the increase ofthe measurement rate and the transmission rate and thus the currentconsumption of the battery-operated system than erroneously remaining inthe parking state, which merely has the effect that starting the vehicleis detected only a short time later. Thus, the error tolerance forchanging from the parking state to the driving state is much lower thanthe error tolerance for remaining in the parking state. This appliesboth for methods where the differentiation between driving state andparking state is made by measuring the centrifugal forces with anacceleration sensor and for a system where a curve of the tire pressuremeasurement values is used for this decision.

Here, as a further example, a method can be used, for example, where nodifference is made between driving state and parking state, but wherethe decision when a measurement value is to be transmitted is deriveddirectly from the curve of the tire pressure measurement values. Here, awrong decision for transmitting causes again a transmission process withhigh current consumption placing a burden on the battery-operatedsystem, while a wrong decision for not transmitting merely causes ashort delay of the transmission process.

Further, it applies that the fulfillment of the criteria, which meansswitching between the driving state and the parking state or thedecision to transmit a measurement value occurs extremely rarelycompared to the time where no decisions are to be made, which means thecontinuous remaining in the driving state or the parking state or nottransmitting measurement values.

The inventive method allows to perform the measurements with exactly theminimum frequency defined by the predetermined maximum allowabledecision delay time, to decide safely whether a criterion is fulfilledand still to require less current.

In an appropriate choice of time intervals between the repetitions, thethreshold exceeding can be reproduced with high probability. Arepetition criterion set up according to the above-described rules cantherefore be fulfilled with high probability. If this criterion isfulfilled, the associated action, e.g. recognizing a transition fromparking state to driving state is performed with an associated increaseof the measurement rate and increased RF transmission of measurementvalues.

Further, the inventive concept can be summarized as follows:

-   -   1. The pressure in the tires is measured at time intervals,        which are shorter than the time period intended for detecting        the transition between non-operated state and driving state.    -   2. A short-term average value of the pressure curve is formed        from the successive pressure measurements by filtering.        -   The difference to the average value is formed from every            measurement value.    -   3. The differences are squared.    -   4. The squares are filtered again to determine a short-term        average value of the squared deviations.    -   5. A transition from a non-operated state to a driving state is        performed when a predetermined number of exceedings of the        current difference squares over a predetermined multiple of the        short-term average value of the different squares occurs within        a predetermined number of measurements.    -   6. In this transition, filtering of the difference squares is        terminated and the last short-term average value of the        difference squares is maintained.    -   7. A transition from the driving state to the non-operated state        is performed when the switching condition from non-operated        state to driving state is not fulfilled within a predetermined        number of measurements.    -   8. After switching back to the non-operated state, filtering the        difference squares for adapting the switching threshold is        activated again.

Variations are:

-   -   (to 1) The measurement times can be different in the driving        state than in the non-operated state. This becomes significantly        easier in the new method, because the adaption of the switching        thresholds is only performed in one of the two states.    -   (to 2,3) The pressure difference is obtained directly from two        subsequent pressure measurements without forming a short-term        average value.    -   (to 4) Instead of the difference squares, difference amounts can        be used.    -   (to 5) The multiple of the short-term average value is limited        by a maximum value to ensure than high pressure deviations,        which are not plausible in the non-operated state, always lead        to a transition to the driving state.    -   (to 5) The multiple of the short-term average value is limited        by a minimum value to ensure that pressure deviations, which are        clearly too low for a driving state, cannot lead to an        unnecessary transition to the driving state.    -   (to 5,6) By grading the multiples and fractions, which are        defined as switching borders, additional states can be defined.        Example: non-operated state, driving (low dynamic), driving        (high dynamic), alarm state.    -   (to 7) The frozen value of the short-term average value of the        difference squares is adapted to the proportionality of the        thermal noise (which should cause the main portion of the        measurement differences in the non-operated state) to the        absolute temperature by a temperature compensation. I.e., in a        temperature increase, the switching threshold, which defines the        transition from the non-operated state to the driving state, is        also raised to make the switching condition independent of the        temperature.

According to a further aspect, the inventive concept can be summarizedas follows:

-   -   1. The system has a switching threshold, and when the same is        exceeded or fallen below, an action is triggered, such as the        transmission of measurement data towards the outside or the        change of a system-internal state, which again, for example,        causes an increase of the sampling rate.    -   2. This switching threshold can also be determined adaptively as        described in (1,2) or can be altered by a timer in a        time-dependent way.    -   3. The noise caused by the sensor system and its characteristic        is known and, thus, an error probability (p_(el)) for the single        measurement results.    -   4. To make a decision with a predetermined maximum allowable        error probability (p_(emax)), a repetition number is calculated        which results from a rounded-off integer quotient of the        logarithms of the two error probabilities.        n=log(p _(el))/log(p _(emax))    -   5. The decision is always repeated when a decision criterion is        fulfilled.        -   If it is not the same in the repetition, the decision is            discarded and the repetitions are terminated.        -   If the decision is the same in the repetition, the            repetition is continued until n repetitions with the same            result are present and then the decision is finally made.        -   The error probability for the n-fold decision is then:            p _(e (n of n)) =p _(el) ^(n).    -   6. The repetitions are only performed when due to a single        decision attempt a decision (example tire pressure sensor:        transition from the parking state to the driving state) would be        made, and this attempt already indicates that probably no        decision would be made, the repetitions can be omitted and the        energy consumption-intensive measurements can be saved.

Variations are:

-   -   (to 5) Not all repetitions have to be the same for the decision        to be made, but a rate is defined that m of n decision attempts        have to be positive.        -   The error probability results as            p_(e (m of n))=p_(el)/(1−p_(el))^(m-n).        -   This variation is particularly useful when the signal to be            decided upon is also random and can occasionally fall to a            value, which would not lead to a decision (e.g.: the            decision whether a vehicle drives or not due to the tire            pressure or due to a measurement of the centrifugal forces            with an acceleration sensor can be wrong time and again due            to short stops even if the vehicle is already driving,            although the vehicle has not been parked again (here,            parking means longer parking)).    -   (to 5) Several thresholds can be defined, which have to occur        with a different frequency in order to lead to a decision (e.g.:        -   1. threshold with 3fold standard deviation has to occur 10            times        -   2. threshold with 4fold standard deviation has to occur 5            times        -   3. threshold with 5fold standard deviation has to occur 2            times).        -   The decision is only finally made when one of the criteria            associated to the different thresholds is fulfilled within a            defined time window.    -   (to 5) As before, different thresholds can be introduced and        points can be associated to every threshold (e.g.:        -   1. threshold with 3fold standard deviation provides 1 point        -   2. threshold with 4fold standard deviation provides 2 points        -   3. threshold with 5fold standard deviation provides 4            points).        -   The points are summed up via a defined time window and the            decision is only really made when a defined minimum number            of points is obtained.    -   (to 5) The time intervals of the repetition measurements have to        be in the same period as the measurements prior to the threshold        exceeding, but can take place faster to ensure a sampling rate,        which is, on the one hand, significantly below the bandwidth of        the superposed noise, but, on the other hand, oversamples the        signal to be detected (e.g. driving-induced pressure changes)        (faster than the Nyquist rate defined by the Shannon sampling        theorem). When the repetition criterion is not fulfilled, a        switch-back to the old sampling rate defined for the parking        state is made. When the repetition criterion is fulfilled, the        increased sampling rate can be maintained or a change to another        sampling rate defined for the driving state can be made.

Depending on the circumstances, the inventive method can be implementedin hardware or in software. The implementation can be on a digitalmemory medium, particularly a disk or a CD with electronically readablecontrol signals, which can cooperate with a programmable computer systemsuch that the corresponding method is performed. Generally, theinvention also consists in a computer program product with a programcode for performing the inventive method stored on a machine-readablecarrier, when the computer program product runs on a computer. In otherwords, the invention can be realized as a computer program with aprogram code for performing the method when the computer program runs ona computer.

While this invention has been described in terms of several preferredembodiments, there are alterations, permutations, and equivalents whichfall within the scope of this invention. It should also be noted thatthere are many alternative ways of implementing the methods andcompositions of the present invention. It is therefore intended that thefollowing appended claims be interpreted as including all suchalterations, permutations, and equivalents as fall within the truespirit and scope of the present invention.

The invention claimed is:
 1. An apparatus for determining a driving situation of a vehicle to be monitored, comprising: a provider configured to provide a plurality of measurement values, wherein the measurement values comprise information relating to the driving situation of the vehicle to be monitored; a comparator configured to compare the measurement values with a predetermined comparison parameter, wherein the comparator is further configured to output a first comparison signal when a predetermined number of measurement values within a measurement interval falls below the predetermined comparison parameter, or wherein the comparator is further configured to output a second comparison signal when the predetermined number of measurement values within the measurement interval reaches or exceeds the predetermined comparison parameter, wherein the first comparison signal or the second comparison signal indicates the driving situation of the vehicle, wherein the driving situation of the vehicle comprises one of a parking state causing a static load condition in the tire and a motion state causing dynamic load changes in the tire, wherein the provider comprises a tire pressure sensor, wherein the provider comprises an evaluator configured to evaluate the plurality of measurement values and provide evaluated measurement values as measurement values in response thereto; wherein the evaluator comprises a determiner configured to determine an average value of the plurality of measurement values, wherein the evaluated measurement values are the differences or the absolute value of the differences between the measurement values and the average value, and wherein the average value of the evaluated measurement values is the predetermined comparison parameter.
 2. The apparatus of claim 1, wherein the determiner comprises a low-pass filter configured to determine the average value by low-pass filtering.
 3. The apparatus of claim 1, further comprising a determiner configured to determine and provide the predetermined comparison parameter.
 4. The apparatus according to claim 3, wherein the determiner is configured to output a multiple of the average value or a fraction of the average value as the predetermined comparison parameter.
 5. The apparatus of claim 3, wherein the determiner is controllable, and wherein the apparatus for determining the driving situation further comprises: a controller configured to control the determiner, wherein the controller is configured to generate a first control signal, in response to which the determiner determines the predetermined comparison parameter, and wherein the controller is further configured to generate a second control signal, in response to which the determiner interrupts a determination of the predetermined comparison parameter.
 6. The apparatus of claim 5, wherein the driving situation is a driving situation of a vehicle, wherein the driving situation comprises one of a parking state and a motion state, and wherein the controller is configured to output the first control signal when the first or the second control signal indicates the parking state, and to output the second control signal when the first or second control signal indicates the driving state.
 7. The apparatus of claim 1, wherein the provider comprises a measurement sensor, and wherein the measurement sensor is a tire pressure sensor or an acceleration sensor, and wherein the driving situation is a driving situation of a vehicle, and wherein the driving situation comprises one of a parking state and a motion state, and wherein the measurement sensor has a first measurement rate in the parking state and a second measurement rate in the motion state, and wherein the first measurement rate and the second measurement rate are different.
 8. The apparatus of claim 1, wherein the measurement interval comprises a time period corresponding to a number of measurement values.
 9. The apparatus of claim 8, wherein the number of measurement values is set.
 10. The apparatus of claim 9, further comprising a determiner configured to determine the number of measurement values.
 11. The apparatus of claim 1, further comprising a determiner configured to determine the predetermined number of measurement values.
 12. The apparatus of claim 1, wherein the driving situation indicates a driving situation of a vehicle, and wherein the driving situation comprises one of a parking state and a motion state, and wherein the first or second comparison signal indicates the parking state, and wherein the other of the first or second comparison signal indicates the motion state.
 13. The apparatus of claim 1, wherein the provider comprises an acceleration sensor.
 14. An apparatus for determining a state parameter of an object to be monitored, comprising: a provider configured to provide a plurality of measurement values, wherein the measurement values comprise information relating to the state parameter of the object to be monitored; a comparator configured to compare the measurement values with a predetermined comparison parameter, wherein the comparator is further configured to output a first comparison signal when a predetermined number of measurement values within a measurement interval falls below the predetermined comparison parameter, or wherein the comparator is further configured to output a second comparison signal when the predetermined number of measurement values within the measurement interval reaches or exceeds the predetermined comparison parameter, wherein the first comparison signal or the second comparison signal indicate the state parameter, and wherein the predetermined number of measurement values is at least two; wherein the provider comprises an evaluator configured to evaluate the plurality of measurement values and provide evaluated measurement values as measurement values in response thereto; wherein the evaluator comprises a determiner configured to determine an average value of the plurality of measurement values, and a subtracter configured to determine a difference between the measurement values and the average value, wherein the evaluated measurement values are the differences or an absolute value of the differences; wherein the determiner is configured to determine an average value of the measurement values, and wherein the average value of the evaluated measurement values is the predetermined comparison parameter; wherein the state parameter is a driving situation of a vehicle, and wherein the driving situation comprises one of a non-operated state and a driving state, and wherein the provider comprises a tire pressure sensor or an acceleration sensor.
 15. The apparatus of claim 14, wherein the determiner comprises a low-pass filter configured to determine the average value of the measurement values by low-pass filtering. 